I am researching MIMO routers for use in a semi truck and figure the people here might know one that will work in my situation.
I really prefer using a hardware NAT device as my first level of security, especially when using a public network. The primary use will be at truck stops and rest areas that offer a wireless feed. Most of the sites I've seen so far only offer 802.11b or .11g so I see no need to get something that also supports a pre-"N" standard unless it's all that is available.
I am looking for a unit that operates on 12 volts DC so I can run it directly off of the truck electrical system. One possible problem is the trucks voltage might swing between 12 to 14 volts depending on what the battery charging system is doing. While on the subject, has anyone used a good 12 volt spike suppressor/regulator for use in a truck or recreational vehicle? I could add something like a 12 volt zener diode in series with the power cable to control the higher voltage swings if nothing else turns up.
Due to the shielding effect of metal trailers a unit that allows for using external antenna(s) would be desired. I plan to mount one or two on antennas on the top of the cab up in the wind deflector. The reason I was looking for a MIMO device was so I could use it as a repeater while taking my laptop outside the truck say at a picnic table.
| I am researching MIMO routers for use in a semi truck and figure the people | here might know one that will work in my situation. | | I really prefer using a hardware NAT device as my first level of security, | especially when using a public network. The primary use will be at truck | stops and rest areas that offer a wireless feed. Most of the sites I've | seen so far only offer 802.11b or .11g so I see no need to get something | that also supports a pre-"N" standard unless it's all that is available. | | I am looking for a unit that operates on 12 volts DC so I can run it | directly off of the truck electrical system. One possible problem is the | trucks voltage might swing between 12 to 14 volts depending on what the | battery charging system is doing. While on the subject, has anyone used a | good 12 volt spike suppressor/regulator for use in a truck or recreational | vehicle? I could add something like a 12 volt zener diode in series with | the power cable to control the higher voltage swings if nothing else turns | up. | | Due to the shielding effect of metal trailers a unit that allows for using | external antenna(s) would be desired. I plan to mount one or two on | antennas on the top of the cab up in the wind deflector. The reason I was | looking for a MIMO device was so I could use it as a repeater while taking | my laptop outside the truck say at a picnic table. | | Any help would be appreciated. |
A 375watt DC-AC inverter can be obtained for as little as $40~45.00 US. Then you will AC for "other" capabilities as well.
Are you sure you're looking for a router and not for a "wireless bridge" or "client radio"? A router is useful for running a server in your truck for others to connect to. It's not useful for connecting to a truck stop hot spot.
Ummm... are you really running a server in the truck?
Ummm... looks like my guess(tm) is correct. You want your truck to connect to the rest stop Wi-Fi feed. For that, you need a wireless bridge or client adapter, not a router.
Purchasing a MIMO client radio will buy you nothing unless the truck stop hot spot has a MIMO router. There are substantial benifits to having a MIMO router, but they will mostly work with non-MIMO clients. Also, there are now about 5 different MIMO implimentations, none of which are compatible with each other. I suggest you drop the MIMO requirement, at least until the 802.11n pissing match, er... standards selection processes, is over and settled. Chances are very high that anything you buy today, with MIMO or Pre-N scribbled on it, will not be compatible with the inevitable 802.11n standards conglomeration.
Running something like a wireless bridge directly off the 12V vehicle system is a bit risky. If you've ever attached an oscilloscope to the cigarette igniter and watched the voltage when the vehicle starts, you'll see 100v or more spikes. You can easily build a suitable filter with some chokes, filter caps, MOV (metal oxide varistors), fuse, and possibly a crowbar protection circuit. A zener or MOV can protect against low energy spikes across the 12VDC line, but will not protect against anything with substantial energy content (such as the back-EMF from the starter). If your tractor starter runs on 24V from two 12V batteries in series, and your accessories run on one of those two batteries, you're going to see a substantial spike on startup.
Methinks a better way is to invest in a DC to DC converter. Most of todays routers, bridges, and wireless contrivances run on 3.3VDC internally. The external power can be anything from 3.3VDC to 12VDC depending on the design of the internal regulator. Something like:
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be worth considering.
Someone suggested a 375watt 12v to 117VAC converter. Well, those get hot, usually have a fan, and are not particularly efficient running a device that only requires about 6-10 watts. Not recommended.
Finding the power requirements for various wi-fi hardware is difficult without ripping open the package and reading it off the wall wart. Sometimes, it's on the manufacturers web pile. More often, it's not. In that case, dig through the disorganized mess on the FCC ID web site. It's always listed on the test report with pictures of the wall wart.
That's going to be impossible with current MIMO technology unless you want to install 3 antennas. Various forms of MIMO use beam forming, beam stearing, or multi-wavefront technologies, that require 2 or more antennas in a well controlled pattern. At this time, there are no external MIMO antenna devices except for some contrivance I recently saw that has the entire RF section in the antenna assembly with a coax??? cable to the PCI board in the desktop computah. I forgot who made it.
There's nothing about MIMO that would prevent you from using a conventional 802.11g device as a repeater. If you drop the MIMO requirement, you have what I've seen on a few trucks and campers. On the roof or any place that's high up, there's a wi-fi repeater of some sorts. In the cab, the owner has a laptop with internal wi-fi. When he arrives at a hot spot, he determines the SSID using Netstumbler (or just reads the sign in the window with the SSID inscribed). He then programs the repeater to repeat that SSID and connects.
One nice feature is that everyone in the area "benifits" from the repeater as other users can connect through it. The bad part is that repeaters create double the number of packets in the air and IMHO constitute a troublesome source of interference. There are also a wide range of access points where repeaters just simply will not work. Compatibility is always an issue with repeaters. I suspect you will have some frustration running a mobile repeater. Not recommended.
What I suggest is you get a rather high gain panel antenna and mount it on a motorized rotator type mount. Only one axis of rotation is required. Install an "ethernet wireless bridge", "game adapter", or "client bridge" type of radio near the antenna (to keep coax cable losses to a minimum). Figure out some way to rotate and aim the antenna. (Yeah, I know it won't work towards the rear if you have a trailer). Plug your laptop into the ethernet (of USB) port of the bridge and connect without a repeater in the way.
I don't know if you can get them off the shelf, but I built a 5V 2A LDO for use with a D-link WAP. The spec on the wall wart was 2A, but mine ran around 1.3A. With a 7V drop, that is 9W. Not trivial, but I don't like all the RF noise from most DC/DC converters.
Dittos on not using an inverter. More RF QRM, plus some devices don't work well off the so-called modified sine wave. I swear I ruined the DC/DC for my notebook by operating it off an inverter.
If you had to go DC/DC, perhaps this would be a better soluti> "GlowingBlueMist" hath wroth:
My thanks to all of you that replied to my questions.
It looks like the MIMO option is off the table for now as I'm sure most of the sites I'll have access to would not actually support the MIMO standard yet. As one mentioned, it sounds like a wireless bridge/repeater may be better suited for what I plan to do anyway.
I can mount an entire wireless access point up on top in a water tight container that is transparent to the proper frequencies.
Yes DC/AC converter might be an option for power but most are quite inefficient and generate quite a bit of heat. I'll hit a few truck stops and talk with drivers that have more than CB antenna's visible and see what they are using. I forgot about the transients caused by the starter, among other things, but they can be handled with the right handfull of components.
Here's another thought. Friend of mine has an always on wap/router with a pcmcia/cardbus data card in it, so he is always connected to the internet via the cellular network (doesn't have to depend on hot spots), and has a repeater mounted on the roof (he's in an rv, airstream - metal roof, wants to be able to use his laptop outside and by the fire :)) When on the road, he's sort of a rolling hotspot :) As an added bonus, using the 1x network, it's fast enuf for voip stuff/and videocalling. He uses it to talk to his family. It's pretty cool/state of the art... for cost, figure about $200 for the hardware, and $79 bucks a month for an always on data card... (powered off a small inverter, $10 at walmart)
(if you want one, click on purchase, you can buy one and have it shipped to you)... The small inverter was because of voltage transients, he didn't want to use the
12vdc built into it, afraid of starting spikes.
In the wonderful land of power supplies, you can literally get any combination of input and output voltage or current. Just don't ask the price. The 2A spec on the wall wart is the nominal operating current, at which the wall wart can operate continuously without catching fire, violating the various certifications, or blowing a fuse. That means it may get a bit warm, or even hot on the larger wall warts, but won't start a fire.
There are many different types of DC to DC converters. The low weight and high efficiency variety operate at 100KHz and up. These generate some RFI which is a problem if you're a ham operator. However, if you don't care about weight, low frequency DC-DC converters work quite well. I once designed a variable pulse width charge pump DC-DC converter, that ran at about 10 Hz. Yep, that's 10 pulses per second. It was terrible at responding to changing loads, but generated no RFI or conducted radiation. Later version used a V-F (voltage to frequency) converter driving the charge pump, which has much better transcient response. There's no magic in these, but they're not commonly available.
I can believe that. A square wave has 33% of its energy in harmonics of the basic 60Hz sine wave. That extra power has to go somewhere. It's about half way dissipated in the low pass filter found on the input circuit of almost all switchers. Get the phase just right, and something is going to smoke. However, if you rip out the low pass, the switchers actually prefer 60Hz square waves to running on 60Hz sine waves. Unfortunately, that's not possible for assorted reasons (switcher stability, tendency to ring, conducted EMI, etc).
With the advent of 3GHz P4 laptops, the power requirements of the battery charger has dramatically increased. I recently had to replace two customers Toshiblah chargers that has blown themselves up. 19VAC at 6.2amps and the size of a small brick. That's about 120 watts. It has to be so big because it should be able to run the laptop with the battery removed. Previous generation of 1.6Ghz Pentium M laptops only had chargers with about half the power output of this monster. If that's what you're running, you don't need an AC inverter to blow one up. They'll do it all by themselves.
That really depends on what the router/bridge/whatever requires. Some of these require 5.0VDC regulated. That's not a typical commodity unregulated 5VDC wall wart with just an xformer and diode inside the case. It's a well regulated power supply, that puts out as close to
5.0VDC as possible.
Fortunately, most routers/bridges/whatevers have internal voltage regulators that can handle a wide range of input voltage and are not particularly critical. The WRT54G is amazing in that it will work from about 4.0VDC to about 18VDC thanks to a nifty internal switcher. I run mine on a 12VDC gel cell and charger. However, most other such devices are not so tolerant.
It's easy enough to measure the input voltage range in the downward direction with an external power supply. The upward direction is the problem. Go too high and you blow it up. Therefore, I trace out the circuit first, identify the components, try to guess the electrolytic voltage rating, and then test the voltage range.
The iGo adapters are the industry standard for road warriors that absolutely hate dragging around a mess of power supplies and cords for their assortment of PDA's, wireless, laptops, cell phones, toys, cameras, and such. One programmable power supply and a collection of adapter tips is all that's required. It's a good system, but in my opinion, rather expensive. It makes sense when one has a variety of devices to power, but not for powering just one in a semi-permanent installation.
The question is does the device really need 2 amps just because the wall wart (or soap on a rope) says 2 amps on it. For products that are not meant to be battery operated, they often pad the current requirement because nobody would want to junk a box that is working fine but is a bit on the high side of supply current.
Pulse skippers (PFM) can have long periods between hits, so they are somewhat like a low frequency charge pump in that respect.
I don't know how what these inverters use as an input, but I designed a tone generator for a guard tone for a modem and generated the tone by filtering a wave that was 1 1 1 0 -1 -1 -1 -1 0. By inserting a flat spot in the sequence, you are reduce the harmonics. The flat spot costs you nothing in hardware since ground is available on the chip.
The AMD chips using SOI are reasonably low power. The intel chips waste power due to the need to run at a higher clock rate (not as well designed architecture) and the reverse biased diodes using as isolation are a waste of power due to their associated capacitance. My 4.4G AMD
64 runs at (I think) 2.6Ghz.
It is possible the switcher is synchronized to the clock in the router. This is a technique used when you design switchers for cell phones as the harmonics are now well defined. However, I much rather have the power supply outside the box since it will interfere less with the hardware.
It is generally not a good thing to run a box outside the normal operating range even if it seems to work. Depending on the architecture of the switcher, it can cause problems that may not be all that obvious, but could stress components.
This makes the assumption that the limiting component is the capacitor. If you have good equipment and access to chip level transistors (such as on a test pattern), you will find that the devices in low voltage integrated circuits are not all that different from EEPROMs, well except that the EEPROM effect should be very small in a switching transistor. That is, you can detect a threshold shift in a component that is stressed enough. It will probably still work, but it's not a good thing. Though the majority of chips I've designed use large geometry devices, I worked at one of these high speed logic companies doing video chips. In very fine geometry processes, not only could you measure a threshold shift due to overvoltage, but the thresholds themselves would get larger as you toggled the device. Generally fine geometry CMOS products are designed so that at full clocking speed the threshold shift will not be significant over a 10 year period.
I agree the Igo is overkill for the project, but if you can't roll your own, it might be a good solution. Still, I don't think dissipating a few watts is all that evil, which is why I generally go linear.
It usually doesn't need the full rating on the wall wart. My WRT54G wall wart says 12V 1A or 12 watts. It only draws about 5.5 watts. That's a good safe margin.
Sure, but who's going to measure the current drain? It also varies somewhat with what the box is doing, temperature, and configuration. The vendors also like to stock one model wall wart and use it on every one of their products.
I did the pulse width modulator regulator design long before pulse skipper chips were available. I think it was about 1980. Incidentally, the pulse skippers are considered a form of PWM regulators. Pulse skippers have the big advantage of belching less ripple. The V to F converter method also belches less hash, but only with a constant load. Whatever works.
If your tone generator ran at 100 watts output, then life would be a bit more complex in simulating the sine wave.
The input filter serves many purposes. The big one is to placate the manifold regulatory agencies that detest having watts of EMI/RFI radiating from their power lines. Various ordeal tests and certification rites are performed to convince them that the power supply is not a transmitter.
The filters are passive and bi-directional. If you want to prevent anything other than 60Hz from leaving the switcher, you also end up with a 60Hz input filter. That works fine with a 60Hz sine wave, but starts to reflect or dissipate some smoke if there is any harmonic content on the input waveform. Such harmonic crud is common with cheap 12VDC to 117VAC inverters. The input low pass reflects much of the harmonic junk, so the inverter has to figure out what to do with the power. Usually, it just heats the switcher xsistors a bit.
If you don't mind, I don't want to get diverted into the Intel vs AMD debate.
Nope. The various models of WRT54G use assorted switching regulator chips. The WRT54G v1.1 in front of me uses an AnaChip 1501-33 chip.
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clocking and no external sync.
I prefer the switcher inside the box where it can be effectively shielded and filtered. That also allows me to provide an unregulated power source. At 3.3VDC internal power, running an external wall wart regulator results in high currents and lots of noise. Also, there's less of a chance of blowing up the box if the regulator is inside, than if the power jack is connected directly to the internal power bus.
Huh? Stress which components? The 1501-33 switcher chip is made to handle +45VDC input maximum. The only part that might be stressed by overvoltage is the input filter cazapitor, which appears to be a 220uf
25VDC device. I used 18VDC as the upper limit because some models of the WRT54G have an input chip capacitor where the rating is not so obvious.
At the low end of the scale, I've run my BEFW11S4v4 for weeks at
4.0VDC input without incident. The efficiency is worse at the low end so the regulator might dissipate a bit more. However, there's no sign of overheating. Incidentally, the board has a reverse voltage protection diode across the wall wart connector.
Correct. See previous paragraph.
I beg to differ. That might be the case if the regulated voltage varied from its nominal 3.3VDC output. That would certainly have an effect on the internal circuitry. However, we're talking about the voltage going to a rather high power and well protected 3Amp regulator. That's not going to blow unless it gets zapped by way too much voltage, or smoked by running too hot. No threshold effects involved.
I didn't suggest a do-it-thyself project. I suggested a commercial DC to DC converter.
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devices that will run directly from 12V, some manner of spike protection and filtering is advised. That will probably need to be do-it-thyself.
you might clarify what exactly you are attempting to do with this setup ?
As others have mentioned, if you pull into a truck stop that has WiFi - then you will need a Wifi CLIENT to connect. This could be the usual laptop or whaterver... a PSP, ???
But, if you are trying to get an "antenna" up on the rig for better access, then your rig still needs to act like a "client", and therefore you are looking for some kind of "bridge" or "repeater" - to give your rig devices access to your local rig AP, which in turn will access the truck stop AP.
The whole issue of 12v is bad, as a simple wireless AP/bridge draws probably less than 10watts, which an inverter would work great - Heck my son drags our small inverter in the car to run the laptop on long trips.
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